1. Preheat oven to 350ºF and lightly grease standard 12-muffin tins with cooking spray. Brown sausage in a frying pan over medium heat for 5 minutes. Drain excess grease if there is any. Add spinach and peppers to pan and cook 5 minutes longer. Cool for 10 minutes.
2. Whisk eggs and soy sauce in a large mixing bowl. Add sausage mixture and cheese. Stir well. Fill muffin tins ¾ of the way full with egg mixture. Bake for 25-30 minutes, until firm in the center. Cool in pan 10 minutes before serving.